Right from the beginning of his Arsenal career, Arsène Wenger has been aware of the particular tension that gnaws at goalkeepers. One of his earliest signings was Alex Manninger, a young Austrian with a strapping physique, terrific reflexes, and bags of potential. What Manninger did not have, however, was big-match temperament. The slightest mistake would antagonise him, and his team-mates soon became used to the sight of him sitting in the dressing room with a towel on his head barking at himself in German.

Arsenal's current custodian shows his torment in a different way. Manuel Almunia is capable of looking so vexed, with the baggage under his eyes causing such strain, it seems he can not have slept for a week. Perhaps he has not. There has been plenty to toss and turn about in between a sobering and error-strewn defeat at home to Manchester United and a visit to a Chelsea team who have slammed seven goals past him in the past two meetings.

Visible nervousness is hardly a useful asset for a goalkeeper. Arsenal's season has been punctuated by individual errors at the back. Not all of them are Almunia's, but sometimes the defenders in front of him lapse in concentration because they appear to be worried about what the man behind them is – or is not – going to do. Will he clear the ball or shank it? Will he come for the cross or stay? Will he catch or flap?

Earlier this season, when Chelsea went through an uncharacteristically vulnerable spell and conceded virtually any time a high ball was hurled into their box, you could sense their defence was similarly uneasy about Petr Cech, whose form hit a rocky patch. Uncertainty is virulently contagious.

As the former double-winning captain Frank McLintock says: "The goalkeeper is absolutely vital. It all starts from there. If he's nice and calm and full of authority it sets everything up in front of him. Almunia has lost confidence in himself. When the ball is knocked back to him he swings at it, he panics."

Even Wenger admits Almunia worries too much. "I think he puts a lot of pressure on his shoulders. Too much," he mused at the training ground last week. "If you look well across Europe you see that goalkeeper is the most difficult job in the world today. And it is even harder in England. Everything is quick, people stand on your feet at crosses. It is a terrible job."

The Frenchman tries to be empathetic. "A goalkeeper is always in a negative publicity. If a striker misses two chances and scores two he is a hero. If a goalkeeper makes a fantastic game and makes one mistake he is a villain. They are under massive pressure because of that fear to make one mistake, knowing that it can kill the team and the game. It is may be the most pressurised job in football."

Almunia's mistakes have been worryingly numerous this season. His ranking, in terms of saves to shots ratio, charts him as 19th in the Premier League. Hardly the foundation required to win titles. Brian Clough used to say that Peter Shilton won him 15 points per season. At some point Wenger has to calculate how many points his keeper is costing him.

Although Arsenal's manager still pledges faith in the Spaniard, the view in the Emirates audience is an overwhelming lack of trust in the club's No1. It is the most hotly debated topic in N5. For how long can he keep his place?

But the trouble is, none of the three young understudies on the books looks ready yet to elbow him out of the way – Lukasz Fabianski has had his own hairy moments, Vito Mannone looked raw when he was promoted earlier this season, and although Wojciech Szczesny (probably the most gifted of the lot) is earning rave reviews on loan at Brentford he is 19 years old and rightly honing his skill.

If there was an argument for strengthening a position of weakness in the transfer window, Wenger didn't want to hear of it.

An eye for a goalkeeper has never been his greatest gift. David Seaman was the perfectly solid base at the club when the manager first arrived, but the selection recruited to emulate him include Manninger, Richard Wright, Rami Shaaban and Almunia, who have all struggled with varying degrees to prove they have nerves for the task. Jens Lehmann, who nobody would accuse of having a nervous disposition, was the exception to that rule, and he was a law unto himself.

Before joining Arsenal in 2004, Almunia had spent the majority of his career in the Spanish second division. Even he did not expect to become first choice for a member of the Champions League establishment. Five years into his time in north London, with nearly 150 Arsenal appearances under his belt, the 32-year-old is still heavily burdened with the pressure of his position.

Wenger has dealt with goalkeepers going through a rotten spell in hardline fashion before. Lehmann never forgave Almunia for stepping in when Wenger suddenly dropped the controversial German. The Arsenal manager is adamant he has no qualms about doing the same again.

"I am not afraid to make a tough decision," he says. "My only target is to make the right decision for the club. But after a game like Sunday we have to believe in our players rather than change half of the team. Almunia has done very well recently. People always look for a scapegoat when you lose a big game, you know."

He then added that Fabianski has "a little issue" with Chelsea after handing their London rivals a gift in the FA Cup semi-final last year, which suggests a change is not imminent. Even so, the Pole is not the only one who must wonder how many more flaps he must watch from a distance before he gets another chance.